The present invention relates to papermaking pulps, papermaking processes employing the pulps, and paper and paperboard products made from the pulps. More particularly, the present invention relates to treating papermaking pulp with at least one microparticle-containing retention aid system.
Microparticles and other particulate materials have been added to papermaking pulps as retention aids. For example, U.S. Pat. No. 4,798,653 to Rushmere, which is incorporated herein in its entirety by reference, describes a papermaking stock including cellulose fibers and a two-component combination of an anionic polyacrylamide and a cationic colloidal silica sol.
One problem with microparticle sols that have been employed in papermaking pulps has been with instability. Because of the instability of sols used in connection with papermaking pulps, the sols are often made on-site for immediate delivery to a papermaking process. A need exists for a stable microparticle sol retention aid for use in papermaking processes which can be formed off-site, exhibits a long shelf life, and can be shipped to a papermaking plant for immediate or future use in a papermaking process.
A need also exists for a papermaking pulp that exhibits even better retention of fines and even better resistance to shear forces during a papermaking process. A need also exists for a papermaking pulp that produces a paper or paperboard product with improved strength characteristics.
The present invention relates to the use of a combination of fibrous cationic colloidal alumina microparticles and at least one polymer as a retention aid system for a papermaking pulp or stock. The fibrous cationic colloidal alumina microparticles can preferably be a cationic fibrous acetate salt of boehmite alumina. The fibrous product can be obtained by stirring a slurry of water and basic alumina acetate to ensure substantially complete mixing thereof, and then reacting the slurry to produce a fibrous cationic acetate salt of boehmite alumina preferably having a zeta potential, when measured in deionized water, of greater than about 25 and preferably having a weight ratio of alumina to acetate of less than about 4. The surface area to volume ratio of the salt is preferably about 50% or greater. The polymer can be a cationic polymer, a nonionic polymer, or an amphoteric polymer used under cationic conditions. The polymer is preferably a synthetic nitrogen-containing cationic polymer, for example, a cationic polyacrylamide. If nonionic, the polymer can be, for example, a nonionic polyacrylamide or a polyethylene oxide.
The present invention also relates to papermaking pulp or stock that includes fibrous cationic colloidal alumina microparticles in combination with at least one polymer as a retention aid system.
Exemplary fibrous boehmite alumina microparticles suitable for use in the retention aid system of the present invention include the fibrous alumina products obtainable by the processes described in U.S. Pat. No. 2,915,475 to Bugosh, and those described in WO 97/41063, which are both incorporated herein in their entireties by reference. The fibrous cationic colloidal alumina microparticles are preferably very stable, preferably have a long shelf life, and preferably can be made off-site and then shipped to a paper mill for future use. The pulps or stocks of the present invention may also contain or be treated with at least one coagulant, at least one flocculant, at least one filler, at least one polyacrylamide, at least one cationic starch, at least one enzyme, and/or other conventional papermaking pulp additives. The resulting pulp or stock is then formed into a wet sheet of pulp or stock having improved retention properties compared to a wet sheet made of conventionally treated pulp. After drainage and drying, the resulting paper or paperboard preferably exhibits excellent opaqueness and/or other physical properties.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are only intended to provide a further explanation of the present invention, as claimed. The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate several exemplary embodiments of the present invention and together with description, serve to explain the principles of the present invention.